In general, the amount of data of video data is large. Therefore, when video data is transmitted to a receiving apparatus, a high-efficiency encoding process is performed. Examples of a high-efficiency encoding scheme are ISO/IEC, MPEG2, and MPEG4 (MPEG: Moving Picture Experts Group). When real-time communication is performed by using such an encoding scheme, a delay is lowered in encoding and decoding.
JP-A-60-162392 discloses an interframe encoding process for an image signal. The technology disclosed in JP-A-60-162392 performs encoding block by block in an N line. However, when motion compensation is performed by using a vector without limit, there is a possibility that an error may move or spread, making it impossible to eliminate the error.
Moreover, JP-A-60-146588 discloses the technology of prohibiting motion compensation using a motion vector during a previously-determined time period for an N line on which encoding has been performed.
The encoding schemes disclosed in JP-A-60-162392 and JP-A-60-146588 use a video transmission scheme which is required to provide a live telecast, or the like, in real time. When video is wirelessly transmitted outdoors, in particular, from a moving unit, a line is sometimes disconnected. With the technologies of JP-A-60-162392 and JP-A-60-146588, it takes some time before the video is restored in the receiving apparatus after the line is recovered.